When rolling metal plate by means of a rolling mill, the deflection of the roll caused by the rolling load may often generate the so-called plate crown: a phenomenon that the thickness of the part near the center (in the width direction) of the plate becomes greater than that of the part near the end (in the width direction) of the plate.
One of rolling mills capable of correcting the plate crown is disclosed in the patent document 1. The rolling mill has the upper and lower work-rolls (or intermediate rolls or backup rolls) which are provided with an S-shaped roll crown, which may be called CVC or others, on the periphery, as shown in FIG. 8, and the pair of rolls relatively move (or shift against each other) in the axial direction. The relative movement of the pair of rolls corresponding to the plate width, profile and others can varies a roll gap properly, as shown in FIGS. 8 (a)-8(c), thereby correcting the plate crown.
Another art of correcting the plate crown by means of the rolls in the similar roll-crown periphery is disclosed in the patent bibliography 2.
The rolls used in the rolling mills as described in the patent bibliography 1 and 2 have roll-crown curves or roll profiles, such as an example shown in FIG. 6. In other words, the whole curve of the roll-crown periphery in such rolls can be drawn as a simple curve of those functions as cubic function or sine function of the axial length of the roll (or the position in the barrel length). For the rolling mill which uses work-rolls with such roll-crown curve, the gaps between the rolls at the surface are distributed as shown in FIG. 7. If the width of the metal plate as material is the narrower, the rolls near the center will receive the heavier load and the more deflection, hence the shift length for the rolls should be increased in the direction as shown in FIG. 8 (c) (a plus shifting (S>0)). On the other hand, if the width of the metal plate material is the wider, the rolls will receive widely distributed load and the deflection will be the less, hence the shift length for the rolls should be increased in the reverse direction as shown in FIG. 8 (b) (a minus shifting (S<0)). Thus the proper shift amount of the rolls varies according to the plate material widths, and the settings of the roll-gaps should be adjusted according to the plate product widths as shown in FIG. 7.
The other example of correcting method of the plate-crown is the art shown in the patent bibliography 3. This bibliography describes (particularly as shown in FIG. 2) a six-high mill, or so-called an HC mill or others, which has a pair of flat (without roll-crowns) rolls, as the upper and lower intermediate rolls, and they are mobile in their axial directions. By moving these intermediate rolls in their axial directions, the edges of the flat rolls will be positioned at the end of the plate product to enhance the bending effectiveness in the work-rolls, thereby correcting the plate-crown.
Another example of such mill, applying rolls with an S-shaped roll-crown in place of the flat rolls above-mentioned, is shown in the bibliography 4.
In addition, the patent bibliography 5 describes other method of rolling, using the work-rolls shaped convergent or taper-ground at one end of the flat rolls without roll-crown, positioning this convergent part to one side of the plate material to be rolled. This bibliography states that this method reduces the contact pressure between such convergent part and the plate material so that the edge-drops, which will be explained below, at the edge of the plate are reduced.
Patent Bibliography 1: JP A S57-91807
Patent Bibliography 2: JP A 2001-252705
Patent Bibliography 3: JP B S62-10722
Patent Bibliography 4: JP A S63-30104
Patent Bibliography 5: JP A S55-77903